The last few decades have seen the rise of a new field of research known as "conservation physiology," in which researchers use endocrine approaches to investigate whether anthropogenic activities are stressful to wild animals. To quantify physiological stress, scientists collect plasma, urine, saliva, and/or fecal samples and see whether variations in hormones--glucocorticoids, in particular--are associated with changes in the external environment.

So far, glucocorticoid fluctuations have been found in a variety of species, ranging from pine martens and hyenas to wolves, elk, and bears. The sources of their stress? Activities related to ecotourism, sports, pastoralism, and even simply the presence of people in the habitat (there are natural sources of stress, too, but those aren't the focus of this particular type of research). While physiological stress responses can be adaptive over the short term, they can have negative impacts on immune and reproductive activity if maintained over the long term. Although these have been documented in species exposed to stressors such as social rivals and lengthy periods of inclement weather, there is less information on the physiological implications of extended exposure to human activities.

Addressing this research gap was the main goal of a group of Spanish researchers working in the Natural Park Montes do Invernadeiro in northwestern Spain. Over a 5-year study period, they collected scat samples left by wildcats (Felis sylvestris) living in the park. Going into the study, the scientists hypothesized that stress levels would be higher in wildcats living in the parts of the park most heavily visited by humans. They also anticipated that the cats would be particularly susceptible to human-induced stress during the part of the year when they were engaged in the most sensitive reproductive activities--specifically, January through May, when the wildcats breed and then gestate their young.

The researchers took advantage of the fact that the park is split into three sections with different levels of human activities. The first zone is open to public visitation and contains both lodges and wildlife classrooms; this receives the greatest number of visitors. The next is a restricted zone where people can visit only on foot and only with a park biologist. Finally, the park also contains an "integral reserve zone" where visitors are not allowed; this area, obviously, receives the least amount of human traffic.

In each of these three zones, the scientists walked survey transects in order to look for wildcat scat, which they distinguished from other species' scat by means of size and shape (in case you are curious, wildcat poo is long, cylindrical, and thick, "with contiguous fragments that fit perfectly"). Because of the time required for digestion and excretion, fecal glucocorticoid levels are associated with the previous day's activities; thus, the researchers compared fecal sample information on any given day with human visitation information (provided by park officials) from the day before. In addition to looking for cortisol metabolites (the chemical components left after glucocorticoids are digested), the researchers also measured levels of three reproductive hormones (testosterone, progesterone, and estradiol) and performed genetic analyses to both confirm that all scat samples were from wildcats, and to determine how many different individuals had been encountered throughout the park.

The researchers were able to collect a total of 110 scat samples over the study period; these belonged to 16 different wildcats. Three variables were found to be most closely related to variations in cortisol metabolite concentrations: progesterone and estradiol levels, and number of visitors. In other words, the most stressed wildcats were those who were primed for reproduction, and also those who lived in the high and (to some extent) low visitation zones. When the researchers plotted cortisol metabolite levels against season, they found that stress hormones peaked in the spring and autumn (during gestation and fall dispersal, respectively), while visitation rates peaked in the spring and summer. The vernal overlap means that wildcats may be particularly negatively affected by the presence of people during the time of year when they are most heavily engaged in reproductive activities.

Unfortunately, the current study was not designed to directly collect information on reproductive success, so further research will be needed to see whether higher levels of stress actually do impact fitness. In fact, there are a number of questions that this study leaves unanswered. Prime among these is the direction of the relationship between glucocorticoids and sex hormones: Does cortisol affect estradiol/progesterone (similar to patterns observed in baboons, Papio anubis), or might elevations in sex hormones drive variations in cortisol? Another unanswered question is whether wildcat stress levels in the high-visitation zone were elevated because of the number of humans they encountered or the way in which the cats were disturbed; after all, in addition to being the busiest area of the park, this zone was the only location where the cats were exposed to cars. Understanding the source of the stress will be important for making appropriate management decisions. Finally, the authors make no mention of whether the focal scat samples were evenly distributed throughout the park, or whether there were indications that the cats were actively avoiding areas with human visitors. Previous studies have indicated that wildcats attempt to avoid anthropogenic activities, and so it is possible that the cats are able to choose home ranges in order to minimize their exposure to people.

(A major aim of conservation physiologists is to facilitate ecotourism while minimizing its negative effects on wildlife. Image courtesy of Spain.net.)

One clear contribution of the study is a demonstration of the potential of the conservation physiology approach. Use of scat samples enabled the researchers to collect quite a bit of information on the wildcats without adding further stress by trapping and handling the animals. Further, molecular techniques enabled the scientists to verify the identity of the scat "providers," not only to the species level but also to the level of individual cats. In the future, scat sampling could be a powerful technique for non-invasively monitoring the health of this and other protected species, measuring population growth and home range size, and examining fluctuations in stress levels in response to any number of environmental perturbations. As the authors write, however, researchers should be careful when applying this method to new animals: "...because many inconsistencies in the glucocorticoid measures are related in part to methodological problems, a careful validation for each species is obligatory."